The subject of the invention is a railroad track switch having stock rails and swingable tongue rails.
The parts of a railroad track system which undergo the most stress are the switches. Ordinarily, the rails of a track system must be non-slidably bound to a foundation, which may comprise ties, concrete base elements, or the like; and therefore switches unavoidably have moving parts, namely tongue rails (also called switch tongues). The switch tongues must be brought into an operating position in which they have the same load-bearing capability as the ordinary track rails. The rails of a track system, in order to enable suitable riding comfort simultaneously with high stability under load, must undergo an elastic deflection when stressed by a train; the deflection in the vertical direction may amount to several millimeters. A switch should not act like a foreign body in a track section, but should have the same static and dynamic characteristics as the rest of the track section, allowing for the fact that trains generally pass over switches at a lower speed.
It is generally not difficult to achieve exact positioning of the stock rails, because these can be fixedly attached to the foundation element (e.g. bedplate, ties, or the like). In contrast, because of the greater difficulty of exactly positioning the switch tongues, movable switch tongues require means of supporting them in the operating position. In ordinary switches, "slide chairs" are provided on which the foot of the switch tongue can slide from an idle position into an operating position and back. In order to provide precise abutment of the switch tongues against the stock rails, the slide chairs are provided with lubricants to minimize friction. This arrangement necessitates substantial consumption of lubricants, as well as a need for regular maintenance. In areas subject to freezing conditions, or particularly alternating freezing and thawing in a single day, there is a risk that the switch tongues will be immobilized by ice so that they must be heated before being operated.
In order to convert the sliding friction between the slide chair and the foot of the switch tongue into rolling friction, it is known to provide rolls. In the first attempts, the rolls were disposed such that the switch tongues were supported by the rolls even in the operating position. This resulted in overloading of the rolls, rendering them inoperable and moreover leaving them in a condition such that they interfered with the functioning of the switch. The next step was to provide the rolls only in regions not acted on by the switch tongues when the latter rested against the stock rails. Such a switch is described in Austrian Patent No. 375,697. Rolls are provided, disposed next to the switch tongues. To move the tongues from their operating position resting against a stock rail, the tongues are raised while rolling over the rolls, so that in each case the movement of the tongues passes through a stage of abutment against the rolls, whereas when the tongues rest against the stock rails they are supported on the customary slide chairs. The rolls themselves are rotatably mounted in their own roll blocks, which may be supported on the ties or the like via spring-loaded plates, plate springs, or the like. Exact vertical and lateral positioning of the roll blocks in relation to the bedplate can be accomplished by screwing to the baseplate, whereby lateral adjustment is accomplished by lateral shifting followed by screw fastening, and vertical adjustment by interposing shim-like intermediate pieces between the roll block and the baseplate. The quality of functioning of a switch of the type described is determined by the exact positioning of the rolls in the vertical and horizontal directions. Once the roll blocks are mounted, the positioning of the roll is essentially invariable, since, e.g., in order to change the horizontal position to a relevant small degree one would require the boring of additional holes in the wooden ties at short separations, causing the holes to merge and be ineffective. Attempts to reposition the roll block by inserting intermediate pieces between the wooden ties and the block can lead to premature damage of the ties and high consumption of ties. Thus with the known system exact positioning is at best difficult and gives rise to excessive time spent by maintenance personnel in the dangerous vicinity of the ties.
European OS No. 0,532,860 A1 discloses a switch in which the roll block is vertically and horizontally translatable. The holding means for the roll block comprises a vertical slot through which a threaded bolt is passed which is slidably disposed in a horizontal slot. In order to achieve horizontal and vertical positioning of the roll block it is necessary to loosen the bolt, move the block to the desired position, and then retighten the bolt. A disadvantage of this arrangement is that additional wedges or the like are required to achieve accurate positioning because, e.g. if the rolls are under load i.e. carry the switch tongues, in order to raise the rolls one must overcome the force of the switch tongues, namely by slightly raising the tongues themselves to allow functioning, i.e. position adjustment, of the rolls. The roll block is then fixed in position by tightening the bolt, in a friction-locking means of fastening. Such fastening means are not capable of withstanding high forces such as arise in rail transport; thus continual readjustments are required if the rolls are to function properly rather than have their function taken over by supplementary "slide chairs".